In various applications, it is desirable to perform amplification of electronic digital and analog signals. In optoelectronic applications, an input electronic signal may be a current generated, for example, by a photodiode. It may be further desired that an amplification process generate an output voltage signal. In order to generate an output voltage signal from an input current signal, a transimpedance amplifier may be utilized.
FIG. 1 depicts an exemplary schematic of a single-ended transimpedance amplifier using bipolar technology. Bipolar transistor 104 is biased via voltage sources 112 and 108. Resistor 114 in feedback configuration from output node 110 of bipolar transistor 104 to input node 116 of bipolar transistor 104 provides improved bandwidth and other amplification characteristics of bipolar transistor 104. Input current 102 is provided to bipolar transistor 104 at input node 116, which generates an output current (not shown) across resistor 106, which in turn generates an output voltage at node 110 across resistor 106.
Typically it is important that a transimpedance amplifier be able to amplify input signals spanning a wide frequency range and therefore that the amplifier exhibit a wide bandwidth. This is useful, for example, in high-speed digital baseband communications channels. One method for increasing the bandwidth of a transimpedance amplifier involves utilizing a current buffer at the input of the amplifier, which decouples the source impedance presented at the input of the amplifier from the feedback resistance, which tends to dominate the transimpedance amplifier's input impedance. A current buffer can significantly lower the transimpedance amplifier's input impedance, reducing the effect of capacitive loading at the input on the bandwidth of the amplifier. For example, U.S. Pat. No. 6,801,084 describes a single-ended transimpedance amplifier where the operational bandwidth of the amplifier is improved through the use of an input current buffer.
However, a single-ended transimpedance amplifier such as that shown in FIG. 1 is not in general well suited to applications where it is necessary to amplify input signals spanning a wide dynamic range, due to the output voltage swing at node 110 reducing the WE of device 104. As the input current, and corresponding output voltage become large, the WE of device 104 is no longer sufficient to maintain class A linear operation and distortion of the output waveform results.